Abrasive cleaning machine

ABSTRACT

A portable abrasive cleaning machine has a hood covering a surface area to be cleaned, means such as motor driven impeller for discharging an abrasive agent against the surface, the abrasive agent being fed to the impeller from a container on the machine and being returned to the container together with any foreign particles cleaned from the surface through a tube communicating with the hood. Air currents obtained from a pressurized air source to which the machine is connected are employed to power the motor, to feed abrasive agent to the impeller, to convey the abrasive agent and particles back to the container and to separate the abrasive agent from the particles which are discharged into a bag filter. An embodiment of the machine for cleaning an area at the intersection of perpendicular surfaces is provided with wheels engageable with both surfaces and adjustable to obtain proper contact between the surfaces and the hood of the machine.

United States Patent 1191 Goto et al.

1451 Sept. 23, 1975 ABRASIVE CLEANING MACHINE [75] Inventors: Toshiho Goto; Dan Yoshida; Akira Yamamoto; Tatsumi Onaka, all of Osaka, Japan [73] Assignee: Hitachi Shipbuilding & Engineering Co. Ltd., Osaka. Japan [22] Filed: Mar. 18, 1974 [2]] Appl. No.: 451,986

[30] Foreign Application Priority Data Sept. 26, 1973 Japan 48-! 12199 Mar. 20, 1973 Japan 48-34209 [52] US. Cl. 51/9 M; 5l/l2 [51] Int. Cl. 824C 3/06; B24C 7/00 [58] Field of Search 51/9, 8 R, 12, 9 M; 1 14/222, 224

[56] References Cited UNITED STATES PATENTS 3,262,228 7/1966 Schenck 51/9 3,380,196 4/1968 Mabille 5l/9 3,566,543 3/1971 Fogle i 5l/9 3,691,689 9/l972 Goff 5l/9 Primary ExuminerDonald G. Kelly Attorney, Agent, or FirmFarley. Forster and Farley [57] ABSTRACT A portable abrasive cleaning machine has a hood covering a surface area to be cleaned, means such as motor driven impeller for discharging an abrasive agent against the surface, the abrasive agent being fed to the impeller from a container on the machine and being returned to the container together with any foreign particles cleaned from the surface through a tube communicating with the hood. Air currents obtained from a pressurized air source to which the machine is connected are employed to power the motor, to feed abrasive agent to the impeller, to convey the abrasive agent and particles back to the container and to separate the abrasive agent from the particles which are discharged into a bag filter. An embodiment of the machine for cleaning an area at the intersection of perpendicular surfaces is provided with wheels engageable with both surfaces and adjustable to obtain proper contact between the surfaces and the hood of the machine.

15 Claims, 8 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of5 3 906 673 US Patent Sept. 23,1975 Sheet 2 Ofs 3,906,673

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US Patent Sept. 23,1975 Sheet 4 of5 3,906,673

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US Patent Sept. 23,1975 Sheet 5 of5 3,906,673

FIG. 7

0 T7 8 d n G s 1 F w #WW w 1 Ho m 7 m nf m a O m A heavily armor himself, making it impossible to achieve,

high efficiency of abrasive cleaning. The method using sand blast has higher efficiency of abrasive cleaning than the method using an air grinder, but the former method makes it necessary to later recover theabrasive agent used, which requires much more time and labor than required in the actual abrasive cleaning operation. In order to reuse the recovered abrasive agent, it is nec essary to separate the rust particles therefrom, sothat high economic effect has not been attained.

Further, in connection with the abrasive cleaning of flat surfaces and corners, there has not been provided a compact closed type (automatic abrasive agent circu lation type) abrasive cleaning machine which has basically solved the problems. This kind of conventional closed type impeller blaster is excessively large in size,

weighing several hundred kilograms, so that it cannot be utilized for the abrasive cleaning of hull blocks described above. a v i i I: I

The present invention i'sintended to solve all these problems and provides an abrasivecleaning machine which is small in size and highly portable. I

An abrasive cleaning machine aecording to" the in vention comprises an abrasive agent slinging device including a hood for covering a surface'of given area to be abrasive cleaned anda drive motorfor a sling impel ler, an abrasive agent aceommodating'sealed container supported by said abrasive agent slinging device and communicating with the sling impeller chamber of said device through an abrasive agent feed path, a communication tube for establishingcommunicationbetween the interior of the upper portion of said container and the interior of said hood, a bleed channel which opens to the interior ofsaid container at' the upper end thereof, means for producing air currents which'flow from the interior of said hood via said communication tube and the interior of the container'to said bleed channel, the arrangement being such that only thoseabrasive agent particles which are slung against the surface to be abrasive cleaned'within saidhood by the impeller of the abrasive agent slinging device are returned to said container by said air currents for circulation for reuse. t

With such abrasive cleaning machine-of the invention, since the slung abrasive agent can be automatia cally recovered and circulated for reuse at the same time as the abrasive-cleaning of a predetermined sur-' face by slinging an abrasive agent thereagainst, it. is possible to carry out the abrasive. cleaning operationrcontinuous ly as much as requiredgbysimply preparing a relatively small amount of abrasive agenLThis means that the entire apparatus is compact and easy to handle since the abrasive agent accommodating container may be small in size- Further, the abrasive agent slung region is'cnclosed with the hood and ;the dust including removed rustas well as the abrasive agent slung from the space within the hood is sucked and collected in the abrasive agent accommodating container. Therefore, by simplyconneeting a bag filter or other suitable dust separating means to the bleed channel extending from said container, the working environment can be maintained sanitary andsatisfactory. Moreover, it is no longer necessary to provide for a dust seal.

To sum up, according to the present invention, there is provided anabrasive cleaning machine which is small in size, light in weight (about 20kg), highly portable and particularlysuitable for the abrasive cleaning of hull blocks. 4 I

Other numerous features and merits of the present invention will be readily understood from the following description of .a preferred embodiment of the invention with reference to theaccompanying drawings.

FIG. 1,is a side' elevation, partly in section, of an abrasive cleaning machine according to the present invention;-.

FIG. 2 is anenlargeddongitudinalsection of the abrasive feeding portion'thereof;

FIG. 3 is a sideelevation, partly in section. of the abrasive returnportion in the case where an ordinary vacuum-cleaner is used instead of a bag filter;

FIG. 4 is a longitudinal section of an on-off valve suitable for the present inventive abrasive cleaning machine; I

FIG. 5 is a-perspective :view showing a handle part and air feed passageways in the case where said on-off valve serves also as one of the grip bars of the handle lever; I 1

FIG. 6 is aside elevation showing how a wheel device is attached to anabrasive cleaning machine ofthe present invention which is designed for cleaning of corners;

FIG."7 is a=transverse elevation showing a rear wheel assembly; and.

FIG. 8, is atransvcrse elevation showing a front wheel construction and 'a hood.

An embodiment of the present invention will now be described with reference to FIGS. 1 and 2.

This machine includes abrasive discharging means in the form of a slinging device 1 having an impeller 3 driven'by an air motor 2, and a hood 4 adapted to enclose a region where an abrasive agent is slung by said impeller 3. The slingingdeviee l is attached to the lower region of a handle lever 5 through the air motor 2. The upper end of the handle lever contains an on-off valve and there is provided a grip bar 6 which serves as an operative member for said on-off valve. High pressure airfrom an air compressor (not shown) flows air. motor 2 via a branch tube 8 and a hose 9.

A container 10 stores an'abrasivc agent and is attached to the slinging device 1 through a piping II which, defines-an abrasive agent feed path 12 for introducingthe abrasive agent into the slinging device 1. Forming the end portion 'of the feed path 12 is a bottomed cylinder 24 located centrally of the impeller 3 and provided. with an abrasive agent outlet port 13 which opens transversely .at right angles to the impeller axis, and with an air nozzle 15 which opens toward said abrasive agent outlet port 13 in a lateral wall opposite said port. This cylinder 24 is attached to the slinging device 1 so that it may be rotated around the impeller axis to change the direction of the abrasive agent outlet port 13.

Further, in said abrasive agent feed path 12, there is provided an air nozzle 16 which opens toward the end of said feed path. The air nozzle communicates with a hose through a vertical path 17 in the lateral wall 14, an annular path 18 surrounding the feed path 12 and a communication path 19, said hose 20 communicating with said branch tube 8. The air nozzle 16 is constituted by a narrow tube 22 extending through the curved outer wall 21 of the piping 11 and communicates with the branch tube 8 through the hose 23.

The abrasive agent in the container, upon opening of a valve 45, flows down the feed path 12, is accelerated by high pressure air currents discharged from the air nozzle 16 and reaches the feed path end, from which it is forced into the rotating impeller 3 through the abrasive agent outlet port 13 by high pressure air currents discharged from the air nozzle 15. The abrasive agent is then slung against a surface 25 within the hood 4 to abrasively clean said surface 25.

A tube 26 establishes communication between the interior of the container 10 at the upper region thereof and the space within the hood 4, and a piping 27 which opens at one end thereof to the upper central region of said container 10 has a filter bag 28 connected to the other end thereof. The piping 27 comprises a tubular portion 32 fixed to a lid 31 adapted to be opened and closed with respect to the container 10 by a hinge 29 and a lock mechanism 30, and comprises a constricted tube portion 34 connected to said portion 32 through a joint nut 33, said portion 32 being provided with an air nozzle 36 which opens to the constricted channel 35 of said constricted tube portion 34 from the upstream side of said constricted channel. The air nozzle 36 is connected to the branch tube 8 through a hose 37. The opening 38 in the container 10 for the tube 26 extends tangentially to the container wall. The opening 39 in the lid 31 for the container 10 is provided with an orifice plate 41 having a small opening 40 at the center thereof.

When high pressure air is blown from said air nozzle 36, the presence of the constricted channel 35 results in a negative pressure being produced in the container 10, while. on the other hand. high pressure air from the air nozzles 15 and 16 is flowing into the hood. Therefore, there is defined a path of flow extending from the hood 4 through the tube 26 to the container 10 and then through the piping 27 to the bag filter 28. Therefore. the abrasive agent slung into the hood 4 hits the surface 25 and then, together with foreign matter including rust removed from the surface 25, is sucked into the tube 26 and guided into the container 10. Because of the presence of the orifice plate 41 and the tangential opening 28, the heavier abrasive agent falls down into the container for recovery or storage therein, while the less heavy foreign matter including the rust is sucked up into the piping 27 and then into the bag filter 28, with the air alone permitted to be discharged into the atmosphere through the bag filter.

FIG. 3 shows an example in which a vacuum cleaner is used as suction means. In this case. the tubular portion 32 may be connected to a vacuum suction cleaner hose 42 through a suitable connection tube 43. The hole left after removal of the air nozzle 36 must be closed by inserting a plug 44.

With the abrasive cleaning machine of the construction shown in FIG. 1, when the valve 45 is closed and the grip bar 6 containing said on-off valve therein is manipulated to cut off the air supply from the flexible tube 7 in order to stop the abrasive cleaning operation. the impeller 3 and the rotor of the air motor 2 will continue to rotate for some time by momentum. As a resuit, the pressure in the feed path to the air motor 2 becomes negative. Since said air feed path is in constant communication with the abrasive agent feed path 12 through the hoses 20, 23 and air nozzles 15, 16, when the pressure in said air feed path to the air motor becomes negative, there is produced a reverse air current flowing from the hood 4 through the abrasive agent feed path 12, air nozzles 15, 16 and hoses 20, 23 to the air motor 2. If sufficicnt time is taken between the closure of the valve 45 and the subsequent closure of the air feed path to ensure that the abrasive agent which exists in the route between the abrasive agent feed path 12 and the impeller 3 is completely slung. there will be no problem; without such precaution, however, there would be the danger of the remaining abrasive agent being borne on said reverse air current and sucked into the air motor to damage the latter. When there is fear that such danger will occur, it is desirable to use an onoff valve designed to cut off both the supply of air to the two channels and the communication between said two channels at the same time in one operation.

An example of such on-off valve is shown in FIG. 4. An on-off valve 46 shown therein comprises a cylindrical body 47, an air feed valve 48, a shut-off valve 49, said valves being rotatable in sliding contact with the inner surface of said body 47; a grip portion rotatable in sliding contact with the outer surface of said body and adapted to operate said air feed valve 48 and shut-off valve 49 at the same time; an air feed inlet tube 53 threadedly connected to one end of said body 47 and containing therein an air feed valve spring 52 for urging said air feed valve 48 against the step surface 51 of the body 47'. and an outlet tube portion 54 formed at the other end of said body. An opening 55 in said outlet tube portion 54 communicates with an air inlet path 56 which is opened and closed by the air feed valve 48, through a path in the shut-off valve 49. A second opening 58 formed in the peripheral wall of the body 47 communicates with said air inlet path 56 only when a valve port 59 formed in the peripheral wall of the shut-off valve 49 communicates with said second opening 58. The air inlet path 56 communicates with the inlet tube 53 only when said air inlet path communicates with a valve port 60 formed eccentrically in the air feed valve 48. Designated at 61 is a pin having its inner end fitted in an opening in the peripheral wall of the air feed valve 48, the outer end of the pin extending through a circumferential elongated opening 62 in the body 47 and being fitted in an opening 62 in the grip portion 50. The pin 61 is prevented from slipping out by an Oring 64. A screw 65 threadedly engaged in the peripheral wall of the shut-off valve 49 has its outer end extending through a circumferential elongated opening 66 in the body and fitted in an opening 67 in the grip portion 50. Therefore, by rotating the grip portion 50, the air feed valve 48 and shutoff valve 49 in the body 47 are simultaneously rotated through the pin 61 and screw 65. The numeral 68 designates a strainer installed in the inlet tube 53.

With the on-off valve 46, the air feed valve 48 is r0- .tated by the grip portion50 to close the air inlet path 56, whereby the supply of air to the opening 55 and also the second opening 58 can be cut off. At the same time, the shut-off valve 49 is rotated in operative connection with the air feedvalve 48 to move the valve port 59 away from the second opening 58 so that communication between the openings 55 and 58 is cut off, Further, when the air feed valve 48 is rotated in the reverse direction until its valve port 60'communicates with the air inlet path 56, the shut-off valve 49 is simultaneously rotated in the reverse direction until its valve port 59 communicates with thesecond opening'58 so that is is possible to feed both openings 55 and 58 with air from the inlet tube 53.

Therefore, by using said on-off valve 46 with its inlet tube 53 receiving the air feed flexible tube 7 shown in FIG. 1, with the opening 55 in the outlet tube portion 54 connected to the air feed path to the air motor 2 and with the secondopening 58 connected to the air feed path to the air nozzles and 16, it is ensured that there will be produced no reverse air current described above when the supply of air is cut off. Therefore, the situation in which the remaining abrasive agent is sucked into the air motor is avoided.

Preferably, the on-off valve 46 may be used in the manner shown in FIG. 5. Thus, a T-tube 69 is connected to the upper end of the handle lever 5 shown in FIG, 1, one end opening in said T-tube being connected to the outlet tube portion 55 of said on-off valve 46, the other end opening receiving a usual grip 70 which closes said openingand cooperates with the grip portion 50 of the on-off valve to form a pair, Thus, communication is established between the opening 55 in the outlet tube portion of the on-off valve 46 and the inner passageway of the handle lever 5. Connected to the inlet tube 53 is said air feed flexible tube 7. Apiping 71 is connected to the second opening 58 and to said hoses and 23 through a T fitting 72. In addition, the inner passageway of the handlelever 5 communicates with the air motor 2 through a flow control valve 73 and hose 9.

The peripheral edge of the hood 4, as shown in FIG. 1, has mounted thereon a skirt 74 of rubber or the like surrounding a region wherean abrasive agent is to be slung, and a brush 75 surrounding said skirt 74. An abrasive cleaning operation is carried out by advancing the abrasive cleaning device in such a condition that said skirt and brush arein contact with the surface to be cleaned. In order to readily maintain'said condition, it is desirable to provide the abrasive cleaning machine with a plurality of wheels for maintaining the level of the hood with respect to said surface 25. In that case, if each wheel is arranged so that its level may be adjusted, it is possible to set the level and attitude of said hood to the optimum condition.

As for an abrasive cleaning machine to be used on a flat horizontal surface to be cleaned, there is no need to elaborate a plan for attachment of a wheel device such as the one described above. However, as for an abrasive cleaning machine for cleaning a corner of a surface to be cleaned which is bent at a right angle, a corresponding specially designed wheel device is required.

Description will be made with reference to FIGS. 68 illustrating an example of an abrasive cleaning machine adapted for the abrasive cleaning of corners. This machine 76 is inclined at an angle of about 45. As shown in FIG. 8, a hood 77 for this machine corresponding to the hood 4 shown in FIG. '1 has its peripheralopening edge bent in a V-shape with the axis extending in the direction of travel of the machine. A skirt and a brush 78 are mounted around said peripheral edge and are adapted to contact a substantially right angled surface 79 to be cleaned from its horizontal portion 79a to vertical portion 7912. Front wheel units 81a and 8112 are mounted on the horizontal and vertical outer ends a and 80b of the substantially right-angled flange 80 of the hood 77.

A rear wheel assembly 84 is mounted on an attachment seat plate 83 inclined at an angle of about 45 degrees for an air motor 82 (see FIGS. 6 and 7) corresponding to the air motor 2 shown in FIG. I. The rear wheel assembly 84 comprises a base 86 having an attachment plate 85 attached to said attachment seat plate 83, a horizontal plane engaging outer wheel unit 87:! mounted on the outer end 86a of said base 86, a horizontal plane engaging inner wheel unit 87]) mounted on a horizontal projection 86b of the base 86, and a vertical plane engaging wheel unit 870 mounted on the vertical outer end 860 of the base 86. A handle lever 88, corresponding to the handle lever 5 shown in FIG. 1, projects from the base 86.

Each of the wheel units 810, 8H2, 87a 870 comprises an attachment plate 89 (FIG. 7) an arm 91 pivotally mounted on a shaft extending parallel to the direction of travel of the abrasive cleaning machine. a wheel support frame 92 attached to the outer end of the arm 91, a wheel 93 journaled on said support frame, a screw shaft 96 pivotally mounted at one end on said attachment plate 89 and extending through an opening 95 formed in said arm 91, and a pair of'nuts 97a and 97b thrcadedly engaged on said screw shaft 96 to clamp said arm 91 for fixing the attitude of the latter at any desired angle. Thus, the level of the wheel 93 of each wheel unit with respect to its attachment plate 89 can be optionally adjusted by loosening or tightening the nuts 97:: and 97b.

The front wheel unit 8111 and horizontal plane engaging rear wheel units 870 and 87b contact the horizontal region 79a of the surface to be abrasively cleaned so as to be rollable in the direction of travel of the machine, while the front wheel unit 811; and vertical plane engaging rear wheel unit 870 contact the vertical region of said surface to be rollable in the direction of travel of the machine. Thus, by moving the abrasive cleaning machine along a corner of said surface with the wheels 93 of the wheel units maintained in contact with the surface 79 as shown in FIGS. 7 and 8, the surface corner surrounded with the brush 78 can be continuously abrasively cleaned. In this case, the level of the wheel 93 of each wheel unit is adjusted so that the brush 78 may be in uniform contact with the surface to be cleaned.

In the above abrasive cleaning operation, it is necessary for an operator who is pushing the machine to manipulate the handle in such a manner as to urge the machine toward the vertical region 7911 of the surface to be cleaned so that the wheels 93 of the wheel units 81!; and 870 may not be disengaged from said vertical region 79b. In order to decrease the labor required in such operation, it is desirable that the wheel 93 of the front wheel unit 8111 which is in contact with the horizontal region 790 of said surface be fixed at some angle biased toward the vertical region 7912 of said surface, as shown in FIG. 8.

In addition, an abrasive cleaning machine according to the present invention may be provided with a powerdriven wheel device.

We claim:

1. An abrasive cleaning machine comprising:

abrasive discharging means including a hood adapted to cover a given area of a surface to be cleaned;

an enclosed container for an abrasive agent, and a feed path for said agent extending from said container to said abrasive discharging means;

a return tube establishing communication between the interior of the upper portion of said container and the interior of said hood, and a bleed channel which opens to the interior of said container at the upper end thereof; and,

means for producing air currents which flow from the interior of said hood to said container via said return tube and from the interior of the container to said bleed channel whereby abrasive agent particles which are discharged against the surface to be cleaned are recirculated to said container by said air currents for rc-use. said means comprising a constructed passage provided in said bleed channel, and an air nozzle for discharging pressurized air toward the downstream side of said constructed passage.

2. An abrasive cleaning machine as set forth in claim 1. including a bag filter connected to the terminal end of said bleed channel.

3. An abrasive cleaning machine as set forth in claim 1, wherein an opening in said container for said return tube is directed tangentially to the peripheral wall of the container. and an opening in said container for said bleed channel is sufficiently smaller than the cross sectional area of the container and is located centrally of the container.

4. An abrasive cleaning machine connectable to a source of working air comprising:

abrasive discharging means including a hood adapted to cover a given area of a surface to be cleaned, an air driven drive motor and an abrasive slinging impeller driven thereby. and means for feeding working air to said air motor; an enclosed container for an abrasive agent, a feed path for said agent extending from said container to said abrasive discharging means. and nozzle means supplied by working air for producing air currents to forcibly feed the abrasive agent to said impeller from said feed path;

a return tube establishing communication between the interior of the upper portion of said container and the interior of said hood, and a bleed channel which opens to the interior of said container at the upper end thereof; and, means supplied by working air for producing air currents which flow from the interior of said hood to said container via said return tube and from the intcrior of said container to said bleed channel whereby abrasive agent particles which are discharged against the surface to be cleaned are recirculated to said container by said air currents for reuse.

5. An abrasive cleaning machine as set forth in claim 4, wherein the means for producing air currents comprises a constricted passage provided in said bleed channel, and an air nozzle for discharging pressurized air toward the downstream side of said constricted passage.

6. An abrasive cleaning machine as set forth in claim 4 wherein said abrasive agent feed path is provided at the terminal end thereof with an oulet port opening radially to said impeller, and said air nozzle means comprises a first air nozzle and a second air nozzle, said first air nozzle being located between the ends of said feed path and being directed toward said terminal end thereof, and said second air nozzle being directed toward said outlet port.

7. An abrasive cleaning machine as set forth in claim 4, wherein said hood is shaped to cover a corner portion of a surface to be cleaned from the horizontal region to the vertical region thereof and said machine is provided with horizontal plane engaging wheel units adapted to roll on the horizontal region of said surface and vertical plane engaging wheel units adapted to abut against and roll on the vertical region of said surface.

8. An abrasive cleaning machine as set forth in claim 7 wherein said horizontal plane and vertical plane engaging wheel units are spaced longitudinally in the direction of travel of the machine, and the horizontal plane engaging wheel units include a pair of such units disposed transversely of the direction of travel of the machine.

9. An abrasive cleaning machine as set forth in claim 7 wherein each of said wheel units is arranged so that the level of its wheel is adjustable.

10. An abrasive cleaning machine as set forth in claim 7 wherein one of the horizontal plane engaging wheel units is disposed so that its rolling direction is inclined toward the vertical region of the surface to be cleaned.

11. An abrasive cleaning machine as set forth in claim 4 wherein said machine further includes a manual push handle having a grip bar, a connection on said grip bar for working air, a working air passage extending through at least a portion of said handle, and an onoff valve which also serves as a portion of said grip bar.

12. An abrasive cleaning machine as set forth in claim 4, wherein working air is supplied to said air motor and to said nozzle means through separate feed paths, an on-off valve communicating with each of said feed paths and with the working air connection, said valve including closure means capable of cutting off the supply of working air to each of said feed paths and simultaneously isolating said feed paths from each other.

13. An abrasive cleaning machine as set forth in claim 4, including a bag filter connected to the terminal end of said bleed channel.

14. An abrasive cleaning machine as set forth in claim 4, wherein the means for producing air currents comprises a constricted passage provided in said bleed channel. and an air nozzle for discharging pressurized air toward the downstream side of said constructed passage.

15. An abrasive cleaning machine as set forth in claim 4, wherein an opening in said container for said return tube is directed tangentially to the peripheral wall of the container. and an opening in said container for said bleed channel is sufficiently smaller than the cross sectional area of the container and is located centrally of the container. 

1. An abrasive cleaning machine comprising: abrasive discharging means including a hood adapted to cover a given area of a surface to be cleaned; an enclosed container for an abrasive agent, and a feed path for said agent extending from said container to said abrasive discharging means; a return tube establishing communication between the interior of the upper portion of said container and the interior of said hood, and a bleed channel which opens to the interior of said container at the upper end thereof; and, means for producing air currents which flow from the interior of said hood to said container via said return tube and from the interior of the container to said bleed channel whereby abrasive agent particles which are discharged against the surface to be cleaned are recirculated to said container by said air currents for re-use, said means comprising a constructed passage provided in said bleed channel, and an air nozzle for discharging pressurized air toward the downstream side of said constructed passage.
 2. An abrasive cleaning machine as set forth in claim 1, including a bag filter connected to the terminal end of said bleed channel.
 3. An abrasive cleaning Machine as set forth in claim 1, wherein an opening in said container for said return tube is directed tangentially to the peripheral wall of the container, and an opening in said container for said bleed channel is sufficiently smaller than the cross sectional area of the container and is located centrally of the container.
 4. An abrasive cleaning machine connectable to a source of working air comprising: abrasive discharging means including a hood adapted to cover a given area of a surface to be cleaned, an air driven drive motor and an abrasive slinging impeller driven thereby, and means for feeding working air to said air motor; an enclosed container for an abrasive agent, a feed path for said agent extending from said container to said abrasive discharging means, and nozzle means supplied by working air for producing air currents to forcibly feed the abrasive agent to said impeller from said feed path; a return tube establishing communication between the interior of the upper portion of said container and the interior of said hood, and a bleed channel which opens to the interior of said container at the upper end thereof; and, means supplied by working air for producing air currents which flow from the interior of said hood to said container via said return tube and from the interior of said container to said bleed channel whereby abrasive agent particles which are discharged against the surface to be cleaned are recirculated to said container by said air currents for re-use.
 5. An abrasive cleaning machine as set forth in claim 4, wherein the means for producing air currents comprises a constricted passage provided in said bleed channel, and an air nozzle for discharging pressurized air toward the downstream side of said constricted passage.
 6. An abrasive cleaning machine as set forth in claim 4 wherein said abrasive agent feed path is provided at the terminal end thereof with an oulet port opening radially to said impeller, and said air nozzle means comprises a first air nozzle and a second air nozzle, said first air nozzle being located between the ends of said feed path and being directed toward said terminal end thereof, and said second air nozzle being directed toward said outlet port.
 7. An abrasive cleaning machine as set forth in claim 4, wherein said hood is shaped to cover a corner portion of a surface to be cleaned from the horizontal region to the vertical region thereof and said machine is provided with horizontal plane engaging wheel units adapted to roll on the horizontal region of said surface and vertical plane engaging wheel units adapted to abut against and roll on the vertical region of said surface.
 8. An abrasive cleaning machine as set forth in claim 7 wherein said horizontal plane and vertical plane engaging wheel units are spaced longitudinally in the direction of travel of the machine, and the horizontal plane engaging wheel units include a pair of such units disposed transversely of the direction of travel of the machine.
 9. An abrasive cleaning machine as set forth in claim 7 wherein each of said wheel units is arranged so that the level of its wheel is adjustable.
 10. An abrasive cleaning machine as set forth in claim 7 wherein one of the horizontal plane engaging wheel units is disposed so that its rolling direction is inclined toward the vertical region of the surface to be cleaned.
 11. An abrasive cleaning machine as set forth in claim 4 wherein said machine further includes a manual push handle having a grip bar, a connection on said grip bar for working air, a working air passage extending through at least a portion of said handle, and an on-off valve which also serves as a portion of said grip bar.
 12. An abrasive cleaning machine as set forth in claim 4, wherein working air is supplied to said air motor and to said nozzle means through separate feed paths, an on-off valve communicating with each of said feed paths and with the working air connection, said valve including cLosure means capable of cutting off the supply of working air to each of said feed paths and simultaneously isolating said feed paths from each other.
 13. An abrasive cleaning machine as set forth in claim 4, including a bag filter connected to the terminal end of said bleed channel.
 14. An abrasive cleaning machine as set forth in claim 4, wherein the means for producing air currents comprises a constricted passage provided in said bleed channel, and an air nozzle for discharging pressurized air toward the downstream side of said constructed passage.
 15. An abrasive cleaning machine as set forth in claim 4, wherein an opening in said container for said return tube is directed tangentially to the peripheral wall of the container, and an opening in said container for said bleed channel is sufficiently smaller than the cross sectional area of the container and is located centrally of the container. 